Fish and Invertebrate Health

A healthy fish rises and feeds as soon as food is added, breathes evenly with its gill covers (opercula) closed between breaths, holds its fins open, and has clear skin with no spots, film or sores. Its behavior is normal for its species: some clownfish rest on the bottom, and longfin forms lie on their side, without being ill (Module 29).

A healthy invertebrate is expanded, colored and attached as is normal for its species. Anemones, clams and corals are covered in Modules 27 to 29.

Observe every animal at least once a day, ideally at feeding, when appetite and breathing are easiest to judge. Record anything unusual with the date and time. A log turns an impression into a record of when a problem began and what changed, which is what a treatment decision requires (Module 7).

A pathogen is an organism that causes disease: a parasite, bacterium or virus. Many pathogens are present at low levels in an established system without causing harm. An outbreak follows when animals are weakened by stress: shipping and handling, aggression, injury, crowding, or poor or unstable water.

New arrivals are the most common source of new pathogens, and the most stressed animals in a system. This is why every new animal is quarantined, kept in a separate system for a period so that any disease becomes apparent before it can spread (Module 23), and why captive-bred animals, which carry fewer pathogens, are preferred (Module 24).

Prevention is therefore mostly husbandry: stable water, appropriate stocking, correct feeding, quarantine and biosecurity. Treatment is needed when prevention has failed.

Check the water first. Rapid breathing, hiding and refusing food are also signs of ammonia, low dissolved oxygen, a temperature swing or a salinity error. Test before you diagnose, and correct the water whatever the diagnosis.

Then read the animal. Note which signs are present, how quickly they appeared, and how many fish, and which species, are affected. White grains like salt point to marine ich. A fine gold, dusty sheen with very rapid breathing points to marine velvet. Thick white mucus points to Brooklynella, especially in clownfish. Red sores with defined edges point to Uronema. Flared gill covers and fin damage point to a bacterial infection.

Signs overlap, and an animal can have more than one disease at once. When the signs don't fit one cause clearly, isolate the animal and treat for the most dangerous likely cause first: velvet and Brooklynella can kill within one to two days, while ich usually progresses more slowly.

Marine ich, Cryptocaryon irritans, appears as white grains like grains of salt on the body and fins. Its life cycle has three stages. The trophont feeds within the skin, protected from treatment. It then drops off and becomes a tomont, which forms a cyst on rock, sand or glass and divides into many new parasites, also protected. These leave as theronts, the free-swimming stage that seeks a new fish. Only the theronts are vulnerable, so treatment must outlast the whole cycle, and a course commonly runs four to six weeks (Module 15).

Control. Ich is controlled with a correctly sized UV sterilizer, which kills theronts carried past the lamp (Module 21). In a bad outbreak, combine it with 5 or 10 micron filter socks to catch free-swimming stages, and increase water movement so that more of them are carried to the UV and the socks. With properly sized UV, ich can usually be controlled, and often eventually eliminated. This works in reef systems, where medication can't be used, as well as in fish-only systems.

Copper. Copper was once the standard treatment for ich and velvet. It's no longer recommended: UV and fine mechanical filtration do the job. Copper is toxic to invertebrates, and any tank, rock, sand or equipment that has ever held it's fish-only for good (Module 23).

Marine velvet, Amyloodinium ocellatum, is a parasitic dinoflagellate that attacks the gills and skin. The first sign is often a dead or dying fish. Affected fish stop feeding, breathe very rapidly and may show a fine, gold or dusty sheen on the skin, finer than the grains of ich. Its life cycle resembles that of ich, with a protected cyst stage and a much smaller free-swimming stage, the dinospore.

Isolate at once. Move affected fish to a hospital container of mature system water with strong aeration (section 8). A freshwater dip, with the water matched to the fish's temperature and pH, removes many of the parasites on the fish, but a single dip isn't a cure, because the cyst stage is protected.

Control. In the display and the hospital container, use 5 micron filter socks, which catch the dinospores that pass a 10 micron sock (Module 15), run correctly sized UV, which reduces their numbers, and keep water moving so they reach both. Add no new fish until the outbreak has ended. Velvet moves in days, not weeks: delay is how fish are lost.

Brooklynella hostilis attacks the gills and skin and is known as clownfish disease, because it's especially common in wild-caught clownfish. Early signs are folded fins and lethargy, followed by a thick white mucus coat and rapid breathing. It can kill a fish within 24 to 48 hours of the first signs. Antibiotics don't treat it; formalin is the most effective treatment, used strictly as directed on the product. Captive-bred clownfish carry it far less often.

Uronema marinum causes red sores, often with a sharply defined edge, and is especially common in chromis and other fish stressed by shipping. It progresses quickly, and fish with open sores have a poor outlook. Isolate affected fish at once.

Formalin safety. Formalin is a solution of formaldehyde: toxic, irritating and a known carcinogen. Wear gloves and eye protection, work in a ventilated area, and use it only in a separate treatment container, never in a display system. It lowers dissolved oxygen, so aerate heavily during treatment.

Signs. The earliest signs are flared gill covers and fast or labored breathing. Fin damage follows, even small: white, cloudy or frayed fin edges, strands hanging from the fins, fins shorter than a few days before, or a white haze on the body. A fish lying on its side and refusing food is in the late stage, when treatment rarely saves it. Don't wait to see whether it worsens.

Before treating, check that the signs aren't a white mucus coat on the skin and gills. That points to Brooklynella, which antibiotics don't treat.

Ciprofloxacin. Fish are treated in a hospital container at 6.5 mg/L. One 500 mg tablet dissolved whole in 500 mL of RO water gives a stock of 1 mg per mL, so 6.5 mL of stock per liter gives 6.5 mg/L. Keep the container dark or covered, because light degrades the drug. Photograph the fins daily and compare them with the previous day.

Duration. Treat for at least five days, even if the fish looks normal sooner. If it's improving slowly, continue for up to ten days. If there's no improvement at day five, the medication is changed.

A hospital container holds an animal that's already sick, unlike quarantine, which holds new arrivals (Module 23). Fill it with mature system water, add aeration and a heater, and keep it at the system's temperature. Never use a mesh container: fine mesh clogs with biofilm, oxygen falls, and the fish suffocates (Module 25).

Ammonia. Medications such as antibiotics kill nitrifying bacteria, so a treatment container has no working biofilter. Add an ammonia neutralizer, test ammonia daily, and change water with system water whenever ammonia rises, dosing the medication only for the new water added.

One medication at a time. Don't add a second medication on top of the first. Don't give methylene blue to a fish that's already struggling to breathe.

Biosecurity. Every tool that enters a treatment container is sterilized before it goes in and again when it comes out, and no water passes between the container and any system (Module 23).

Anemones. A limp anemone with a slack or gaping mouth, often with cloudy water after lights out, has a bacterial infection, treated with Ciprofloxacin at a dose that depends on the species (Module 29).

Giant clams. A pinched mantle has several possible causes, of which pinched mantle disease is treated with a freshwater dip (Module 28). Perkinsus, a protozoan parasite of clams, causes a mantle that doesn't extend fully, slow responses to shadow and touch, and sloughing of the byssal tissue in the days before death. There's no treatment. Clams that show these signs don't recover, so symptomatic clams are euthanized with ethanol rather than left to decline in the system. Perkinsus spreads through water and equipment, so strict biosecurity is the only protection (Module 23).

Corals. Tissue necrosis, the loss of tissue from the skeleton, is called rapid tissue necrosis (RTN) when it moves quickly and slow tissue necrosis (STN) when it moves slowly; its cause isn't fully understood, and it's often linked to a stress event such as a temperature spike. Tissue loss isn't always disease. Allelopathy (Module 24), nutrients bottoming out at zero nitrate or phosphate (Module 17), a parameter swing, handling, stings from neighbors and pests (Module 31) all cause it, so diagnose before treating. A failing colony can sometimes be saved by cutting it at least 1.3 cm ahead of the dying tissue.

Brown jelly disease covers large-polyp corals with a brown, jelly-like mass. Remove the jelly with a turkey baster, then treat the coral with Ciprofloxacin at 1 mg/L in a treatment container. When several corals in a display are affected and can't be removed, the low in-system dose used for anemones can be applied to the whole display: 0.125 mg/L every 12 hours for 7 to 14 days, watching every animal throughout (Module 29). Black band disease is a dark band, a mat of microorganisms, that moves across a colony and leaves bare skeleton behind.

Begin with the water: ammonia, dissolved oxygen, temperature and salinity. A water problem can cause every sign in this module, and it weakens animals so that pathogens take hold. Correct it whatever else is found.

Then read every animal. One sick fish suggests an individual problem; several species at once suggests the water or a contagious parasite. Note how quickly signs appeared: velvet and Brooklynella move in one or two days, ich and most bacterial infections over several.

Isolate and treat early, with the treatment that fits the cause. Then correct what allowed the outbreak: a new arrival that skipped quarantine, a stressful move, aggression or unstable water. Most outbreaks have more than one cause.